U.S. patent application number 09/986022 was filed with the patent office on 2002-12-19 for apparatus for manufacturing an optical fiber soot, and method for manufacturing an optical fiber soot using the same.
This patent application is currently assigned to The Furukawa Electric Co, Ltd.. Invention is credited to Arima, Kiyoshi, Kuwabara, Masahide, Toda, Sadayuki.
Application Number | 20020189298 09/986022 |
Document ID | / |
Family ID | 19013425 |
Filed Date | 2002-12-19 |
United States Patent
Application |
20020189298 |
Kind Code |
A1 |
Arima, Kiyoshi ; et
al. |
December 19, 2002 |
Apparatus for manufacturing an optical fiber soot, and method for
manufacturing an optical fiber soot using the same
Abstract
An apparatus for manufacturing an optical fiber soot according
to a VAD method, in which a cross-section shape of a combustion
nozzle of a side burner for heating a core portion is rectangular.
A method for manufacturing an optical fiber soot using the
apparatus.
Inventors: |
Arima, Kiyoshi; (Tokyo,
JP) ; Kuwabara, Masahide; (Tokyo, JP) ; Toda,
Sadayuki; (Tokyo, JP) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
The Furukawa Electric Co,
Ltd.
Tokyo
JP
|
Family ID: |
19013425 |
Appl. No.: |
09/986022 |
Filed: |
November 7, 2001 |
Current U.S.
Class: |
65/531 ;
65/414 |
Current CPC
Class: |
F23D 14/56 20130101;
C03B 2207/54 20130101; Y02P 40/57 20151101; C03B 37/0148 20130101;
F23C 2900/9901 20130101; F23D 14/22 20130101; F23D 14/84
20130101 |
Class at
Publication: |
65/531 ;
65/414 |
International
Class: |
C03B 037/018 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2001 |
JP |
2001-171701 |
Claims
What is claimed is:
1. An apparatus for manufacturing an optical fiber soot according
to a vapor-phase axial deposition method, wherein a cross-section
shape of a combustion nozzle of a side burner for heating a core
portion is rectangular.
2. The manufacturing apparatus according to claim 1, wherein a
width of a rectangular cross-section of the combustion nozzle of
the side burner is 0.7 times or more the diameter of the core
portion.
3. The manufacturing apparatus according to claim 1, wherein a
length of a tapered portion of the core soot tip portion is
controllable, by changing a height H of the rectangular combustion
nozzle of the side burner.
4. The manufacturing apparatus according to claim 1, wherein the
rectangular combustion nozzle of the side burner is separated left
and right at the center thereof.
5. The manufacturing apparatus according to claim 4, wherein a
baffleplate is provided at the center of the rectangular combustion
nozzle of the side burner, to separate a flame of the side burner
left and right.
6. The manufacturing apparatus according to claim 1, wherein at
least two layers of combustible gas are formed in the side
burner.
7. The manufacturing apparatus according to claim 1, wherein the
length of the tapered portion of the core soot tip portion is
controllable, by changing the nozzle tip shape (height of taper) of
the burner hood to be attached to the burner tip portion of the
side burner without changing the burner shape.
8. The manufacturing apparatus according to claim 7, wherein a
height h of a hood outlet of the burner hood to be attached to the
burner tip portion of the side burner is 0.5H or greater, to a
height H of the burner.
9. A method for manufacturing an optical fiber soot, comprising
using an apparatus for manufacturing an optical fiber soot,
wherein, in the apparatus according to a vapor-phase axial
deposition method, a cross-section shape of a combustion nozzle of
a side burner for heating a core portion is rectangular.
10. The manufacturing method according to claim 9, wherein a width
of a rectangular cross-section of the combustion nozzle of the side
burner is 0.7 times or more the diameter of the core portion.
11. The manufacturing method according to claim 9, wherein a length
of a tapered portion of the core soot tip portion is controllable,
by changing a height H of the rectangular combustion nozzle of the
side burner.
12. The manufacturing method according to claim 9, wherein the
rectangular combustion nozzle of the side burner is separated left
and right at the center thereof.
13. The manufacturing method according to claim 9, wherein at least
two layers of combustible gas are formed in the side burner.
14. The manufacturing method according to claim 9, wherein the
length of the tapered portion of the core soot tip portion is
controllable, by changing the nozzle tip shape (height of taper) of
the burner hood to be attached to the burner tip portion of the
side burner without changing the burner shape.
Description
FIELD
[0001] The present invention relates to a method for manufacturing
an optical fiber soot. The present invention also relates to an
apparatus for manufacturing an optical fiber soot.
BACKGROUND
[0002] A vapor-phase axial deposition method (VAD method) comprises
a step in which a part of core and clad of an optical fiber
(hereinafter referred to as core clad) is synthesized by depositing
glass fine-particles, formed in an oxyhydrogen flame, in the axial
direction. The deposit synthesized by this method is called core
soot. The pulling the resultant soot up in the axial direction is
carried out such that the distance between the position of soot tip
portion and a core burner is kept constant. The speed for pulling
the soot up is called growth speed. An apparatus for use according
to this method is schematically illustrated in FIG. 1. A core 1
portion is synthesized by using a core burner 2, and a core clad 3
is synthesized by using a clad burner 4. To heat the core portion
and prevent cracking, and to inhibit interference between the flame
of the clad burner and the flame of the core burner, a side burner
5 is provided at the middle part between the core portion and the
clad portion. The number 6 indicates a bar of starting material for
soot deposition, which is generally a solid bar of quartz and which
is pulled up in the upward direction 8 (direction of pulling up)
while being rotated in the direction (direction of rotation)
indicated by an arrow 7. In FIG. 1, V indicates the length of the
tapered tip portion of core soot.
[0003] The side burner 5, which is conventionally used, has a
structure of a multiple-pipe burner 15 having a circular cross
section, as shown in FIG. 2. FIG. 2 illustrates the cross section
of the conventional burner 5, which has an outer diameter (width)
D, and which has an outer pipe, an intermediate pipe, and an inner
pipe, indicated by 15a, 15b, and 15c, respectively. Generally,
hydrogen gas blows off from the inner pipe, oxygen gas blows off
from between the outer pipe and the intermediate pipe, and argon
gas blows off from between the intermediate pipe and the inner
pipe, so that the combustion flame of the side burner 5 is
formed.
[0004] To raise the productivity according to the VAD method, it is
effective to increase the diameter of the core portion. The
increase of the diameter of the core portion proportionally
increases the area to be heated by the side burner, in particular
the area in the horizontal direction (the area of the cross section
having a diameter (diameter of the core to be heated by the side
burner) indicated by d in FIG. 1). Therefore, to heat evenly the
cross-section portion of the core inside in the horizontal
direction, it is necessary to spread the flame.
[0005] The flame of a conventional burner can be spread by
increasing the amount of gases (combustible gas and
combustion-improving gas). However, since the surface temperature
of the core portion is raised locally, there are such problems that
striae are strengthened to an extent that profile measurement using
a profile analyzer (hereinafter abbreviated as PA) becomes
impossible, or alternatively, that bubbles are formed in the core
preform after making it transparent (sintering). On the other hand,
to prevent unevenness of the surface temperature of the core
portion, if the diameter of the burner is increased, the flame is
spread also in upward and downward directions. Because of this,
interference between the flame of the side burner and the flame of
the clad burner is increased, and the core soot is deformed in the
worst case. To prevent this problem, if the position of the clad
burner is shifted upper, the length V of the tapered portion of
core soot tip portion becomes larger, and the proportion of
defective portions in the resultant core soot increases.
SUMMARY
[0006] The present invention is an apparatus for manufacturing an
optical fiber soot according to a vapor-phase axial deposition
method, in which a cross-section shape of a combustion nozzle of a
side burner for heating a core portion is rectangular.
[0007] Further, the present invention is a method for manufacturing
an optical fiber soot using the above apparatus for manufacturing
an optical fiber soot.
[0008] Other and further features and advantages of the invention
will appear more fully from the following description, take in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a view to illustrate the manufacturing of an
optical fiber soot according to a VAD method.
[0010] FIG. 2 is a cross-sectional view of a conventional
multiple-pipe burner for use in a VAD method.
[0011] FIG. 3 is a cross-sectional view of a multiple-pipe burner
for use in an apparatus of the present invention for manufacturing
an optical fiber soot.
[0012] FIG. 4 is a graph illustrating the relationship between the
diameter D and height H of the burner and the length V of the
tapered tip portion.
[0013] FIG. 5 is a graph illustrating the relationship between the
width L of the burner and the temperature difference .DELTA.T.
[0014] FIG. 6 is a view illustrating a cross-section of another
example of the multiple-pipe burner for use in an apparatus of the
present invention for manufacturing an optical fiber soot.
[0015] FIG. 7 is a view illustrating a cross-section of still
another example of the multiple-pipe burner for use in an apparatus
of the present invention for manufacturing an optical fiber
soot.
[0016] FIG. 8(a) and FIG. 8(b) illustrate an example of the shape
of the tapered tip portion of the side burner, in which FIG. 8(a)
is a top view and FIG. 8(b) is a side view.
[0017] FIG. 9 is a graph illustrating the relationship between the
length h of the hood outlet and the length V of the tapered tip
portion.
DETAILED DESCRIPTION
[0018] According to the present invention there are provided the
following means:
[0019] (1) An apparatus for manufacturing an optical fiber soot
according to a VAD method, wherein a cross-section shape of a
combustion nozzle of a side burner for heating a core portion is
rectangular.
[0020] (2) An apparatus for manufacturing an optical fiber soot
according to item (1), wherein a width of the rectangular
cross-section of the combustion nozzle of the side burner is 0.7
times or more the diameter of the core portion.
[0021] (3) An apparatus for manufacturing an optical fiber soot
according to item (1) or (2), wherein a length of a tapered portion
of the core soot tip portion is controllable, by changing a height
H of the rectangular combustion nozzle of the side burner.
[0022] (4) An apparatus for manufacturing an optical fiber soot
according to item (1), (2), or (3), wherein the rectangular
combustion nozzle of the side burner is separated left and right at
the center thereof.
[0023] (5) An apparatus for manufacturing an optical fiber soot
according to item (1), (2), or (3), wherein at least two layers of
combustible gas are formed in the side burner.
[0024] (6) An apparatus for manufacturing an optical fiber soot
according to any one of items (1) to (5), wherein the length of the
tapered portion of the core soot tip portion is controllable, by
changing the nozzle tip shape (height of taper) of the burner hood
to be attached to the burner tip portion of the side burner without
changing the burner shape.
[0025] (7) A method for manufacturing an optical fiber soot that
uses the apparatus for manufacturing an optical fiber soot as
described in any one of items (1) to (6).
[0026] Referring now to the preferred embodiments illustrated in
the drawings, the apparatus for manufacturing an optical fiber soot
for use in the present invention will be explained in detail.
[0027] According to the first embodiment of the present invention,
in the apparatus for manufacturing an optical fiber soot according
to a VAD method, as illustrated in FIG. 1, a rectangular burner as
illustrated in FIG. 3 is used as the side burner 5 in place of a
conventional multiple-pipe burner having a circular cross-section
(FIG. 2). In the cross-sectional view, a rectangular burner 30 has
a width of L and a height of H, and composed of, for example, an
oxygen gas nozzle 31, an argon gas nozzle 32, and a hydrogen gas
nozzle 33.
[0028] According to another embodiment of the present invention, as
shown in FIG. 6, interference between the core burner flame and the
side burner flame can be inhibited, by disposing a baffleplate,
which separates the gas stream, at the burner center so as to
separate the flame left and right. Heretofore, although it has been
important to stabilize the core burner flame to secure a stable
production in a VAD method, the interference between the side
burner flame and the core burner flame constituted one of the
destabilizing factors. The interference can be avoided if the side
burner is separated from the core burner. However, if the side
burner is separated too much from the core burner, cracks are
formed on the resultant optical fiber soot. Contrary to the above,
in the case of a rectangular burner, since the flame is spread in a
horizontal direction so that the periphery of the core portion can
be heated, thereby the core section can be sufficiently heated even
if a flame is absent in the portion right above the core burner
flame.
[0029] What is described in the above will be explained referring
to FIG. 6 in more detail. FIG. 6 is an illustrative sectional view,
taken along line A-A, of the apparatus for manufacturing an optical
fiber soot of FIG. 1, and is a view shown in the direction of an
arrow A. In FIG. 6, 40 is a rectangular side burner having a
cross-sectional shape as illustrated in FIG. 3, and 41 is a
baffleplate having a width of L1. 42 is a side burner flame, 43 is
a core burner disposed below the side burner, and 44 is a core
burner flame. 45 is a cross section of a core to be heated by the
side burner and the core burner. The degree of the separation of
the flames can be changed by adjusting the width L1 of the
baffleplate 41. Heretofore, the fluctuation in the growth speed was
about 4 mm/hr, but the fluctuation could be reduced to about 1
mm/hr by using this burner according to one embodiment of the
present invention.
[0030] Still another embodiment of the present invention is
illustrated in FIG. 7. In the initial stage of core soot formation,
it is necessary to maintain the core soot and the surface of the
bar of starting material for soot deposition at a high temperature,
so as to enhance the adhesion between the core portion and the bar.
When using the burner of FIG. 6, since the flame is not in direct
contact with the bar of starting material, a relatively large
amount of combustible gas and combustion-improving gas is necessary
so as to raise the temperature. Therefore, according to an example
illustrated in FIG. 7, a layer, which can flow a combustible gas in
the center of the burner is provided, so that the temperature of
the flame center can be raised. According to this construction, the
temperature of the core soot and the bar of starting material for
soot deposition can be raised by use of a relatively small amount
of gases. Besides, if the diameter of the core portion is
increased, the same effect as that of the burner of FIG. 6 can be
obtained by reducing the flow rate of the combustible gas in the
central layer.
[0031] According to this example, the inside of the side burner 40
is separated into a first combustible gas layer 48 at the center,
and a second combustible gas layer 49 at the periphery portion. 46
indicates a first layer of the side burner flame, and 47 indicates
a second layer of the side burner flame. Similarly in FIG. 6, FIG.
7 is an illustrative sectional view, taken along line A-A, of the
apparatus for manufacturing an optical fiber soot of FIG. 1. The
reference symbols in FIG. 7 each indicate the same parts or members
as in FIG. 6.
[0032] FIGS. 8(a) and 8(b) illustrate an example of a shape of the
tapered tip portion of the side burner, in which FIG. 8(a) is a top
view and FIG. 8(b) is a side view. In FIGS. 8(a) and 8(b), a hood
51 to be attached to the tip portion of a side burner 50 takes the
shape of a tapered portion 51a that tapers off toward the tip
thereof, so as to reduce the spread of the side burner flame in
upward and downward directions. This method can also reduce the
spread of the side burner flame in upward and downward directions,
and enables shifting lower the position of the clad burner in the
apparatus. In the figures, H is a height of the rectangular burner,
and h is a height of the tip portion of the tapered portion 51a of
the burner hood. Similarly in FIG. 3, L is the width of the
rectangular burner.
[0033] According to the apparatus and method using the apparatus of
the present invention for manufacturing a soot for optical fibers,
the proportion of defective portions of the resultant core soot can
be reduced in the production process of the soot for optical
fibers.
[0034] According to the apparatus of the present invention for
manufacturing an optical fiber soot, it is possible to heat evenly
the core portion surface and prevent occurrence of bubble in a core
preform after sintering of the soot. Further, according to the
apparatus of the present invention for manufacturing an optical
fiber soot, the flame cannot be spread upward and downward even if
the burner diameter is increased, and the interference between the
flame of the side burner and the flame of the clad burner can be
prevented.
[0035] The apparatus of the present invention for manufacturing an
optical fiber soot exhibits the following functions and effects of
the invention.
[0036] (1) Since a flame uniform in a horizontal direction can be
formed, the surface temperature of the core portion can be
controlled approximately uniformly.
[0037] (2) The spread of the side burner flame in upward and
downward directions can be reduced by narrowing the width of the
burner in a vertical direction. Because of this, since the position
of the clad burner can be shifted lower in the apparatus, the
length V of the tapered portion of core soot tip portion can be
shortened.
[0038] (3) The interference between the side burner flame and the
core burner flame can be reduced, by separating left and right the
rectangular combustion nozzle of the side burner at the center of
the nozzle. As a result, the core burner flame can be
stabilized.
[0039] (4) The temperature at the flame center of the side burner
can be raised, by forming at least two layers of the combustible
gas for the side burner. As a result, the amount of the combustible
gas and combustion-improving gas for heating the bar of starting
material for soot deposition can be saved.
[0040] According to the apparatus of the present invention for
manufacturing an optical fiber soot, it is possible to manufacture
a high-quality optical fiber soot in an efficient manner.
[0041] The present invention will be explained in more detail
referring to the following examples, but the invention is not
limited thereto.
EXAMPLES
Example 1
[0042] Core soot production test according to a VAD method with the
basic structure, as shown in FIG. 1, was conducted using the burner
of FIG. 2 or FIG. 3 as a side burner. In the case of a conventional
burner of FIG. 2 (in which the burner outer diameter (width) of D
was 0.5d wherein d was a core portion diameter), profile
measurement of 9 cores out of 10 cores obtained was impossible by
PA because of excessively large striae. Besides, in the cores whose
profiles could be measured, bubbles were occurred along the entire
length of the obtained core.
[0043] On the other hand, in the case where the rectangular burner,
as illustrated in FIG. 3, was used, no bubble occurrence was
observed and profile measurement could be made, when a
multiple-pipe burner having the width enlarged to 0.7d was
used.
Example 2
[0044] Then, tests were conducted with respect to the length V of
the tapered tip portion, as illustrated in FIG. 1. The length of
the tapered tip portion of the soot resulting from a conventional
burner (see FIG. 2) was defined to be V.sub.0. The length of the
tapered tip portion of the soot became longer and was 1.7V.sub.0,
when the position of the clad burner was shifted upper using the
conventional burner of FIG. 2. Then, the rectangular side burner of
FIG. 3 was positioned such that the width having a larger Length
was in a horizontal direction and the width L of the burner was
fixed to 0.7d. Using the rectangular side burner, synthesis was
conducted by changing the height H of the burner according to two
levels, i.e., 0.5d and 0.3d. As a result, the lengths of the
tapered portion of the resultant soot could be shortened and were
V.sub.0 and 0.7V.sub.0, respectively. No bubble formation was
observed and profile measurement could be made. This relationship
is shown in FIG. 4.
[0045] The surface temperature of the core portion while being
synthesized was measured. The temperature distribution of the core
portion in contact with the flame of the side burner in a
peripheral direction was examined. As shown in FIG. 5, the
difference .DELTA.T between the maximum temperature and the minimum
temperature was about 200.degree. C. in the case of the
conventional burner of a circular cross-section, but the difference
could be reduced to 100.degree. C. or less in the case of the
rectangular burner according to the present invention.
[0046] Furthermore, the temperature of the core portion in contact
with the flame of the side burner in a peripheral direction was
examined with the rectangular burner by varying the width L of the
burner. As is apparent from FIG. 5, when the width L became smaller
than 0.7d to the diameter of the core portion, the resultant
.DELTA.T became abruptly larger. Based on this result, it can be
understood that it is preferable that the width L of the
rectangular burner is 0.7d or greater to the diameter d of the core
portion.
Example 3
[0047] An example in which a burner hood of FIGS. 8(a) and 8(b) was
used is described below. FIG. 9 is a graph illustrating the
relationship between the height h of the hood and the length V of
the tapered portion of the core soot tip portion when the height h
was varied while the height H of the burner was unchanged. As is
apparent from FIG. 9, the length V of the tapered portion of the
core soot tip portion could be reduced by lowering the height of
the hood outlet. This method is economical because the length (V)
of the tapered portion of the core soot tip portion can be
controlled by exchange of the burner hood. Besides, the hood tip
portion could be used in a normal state without being burnt, if the
height h of the hood outlet was 0.5H or greater, to the height H of
the burner.
[0048] Having described our invention as related to the present
embodiments, it is our intention that the invention not be limited
by any of the details of the description, unless otherwise
specified, but rather be construed broadly within its spirit and
scope as set out in the accompanying claims.
* * * * *